The film will feature contributions from Prince William and Prince Harry, who both speak openly about their mother and how she has influenced their lives.

Their Royal Highnesses will also offer their perspective on Diana's contribution to public life, including her charitable and humanitarian work. Topics such as child bereavement, homelessness and HIV and AIDS will be explored.

The documentary was commissioned for ITV by Jo Clinton-Davis, Controller of Factual and Sue Murphy, Head of Factual Entertainment.

Clinton-Davis said: “This new ITV film will offer viewers a fresh and revealing insight into Princess Diana through the personal and intimate reflections of her two sons and of her friends and family, many of whom have never spoken before, to bring together a definitive portrait of a unique person who touched the lives of millions.”

The film’s Executive Producer Nick Kent said: “This film will show Princess Diana in a way she has never been seen before, through the eyes of the two people who knew her best.”

The documentary will be broadcast on ITV later this year.